In recent years, shifting to aqueous systems has been examined actively in coating materials and the like, due to environmental problems, danger of fires and the like, and regarding pigment anti-settling agents, naturally, aqueous ones are also sought. For instance, in solvent-based coating materials, the use of a heat-treated amide wax-based (Patent Document 1) or hydrogenated castor oil-based anti-settling agent (Patent Document 2) is well known for the purpose of preventing settling of pigments. While many of these additives demonstrate excellent pigment anti-settling effects under an ordinary temperature environment and under a high-temperature environment such as at 50° C., they are not fit for an aqueous system due to poor affinity for water.
Meanwhile, a polyamide-based aqueous anti-settling agent containing a polyamide obtained by reacting a primary diamine having specific numbers of carbon atoms and dimer acid (Patent Document 3), an aqueous anti-settling agent containing a polyamide, which is obtained by reacting a diamine with 14 to 40 carbon atoms and a dicarboxylic acid with 2 to 22 carbon atoms, and a polycondensed polyester having a hydroxyl group (Patent Document 4), and an aqueous anti-settling agent containing a polyamide, which is obtained by reacting a diamine with 4 to 40 carbon atoms and a dicarboxylic acid with 4 to 40 carbon atoms, a polyolefin wax and a surfactant (Patent Document 5) are known. However, while polyamide-based aqueous anti-settling agents demonstrate excellent anti-settling effects under ordinary temperature environment, they have the disadvantage that the pigment anti-settling effects are poor under a high-temperature environment such as at 50° C., for instance.
As described above, various aqueous anti-settling agents have been proposed in prior art. However, for instance, aluminum pigments or pearlescent pigments such as mica used in aqueous metallic paints, or corrosion-resistant pigments contained in aqueous corrosion-resistant paints, or the like, have large particle size and large specific gravity as well, such that, regarding these paints, an aqueous anti-settling agent, even if it demonstrates sufficient effects under an ordinary temperature environment, it has problems such as, the effects are insufficient under a high-temperature environment such as at 50° C., which is the heat-resistance temperature required in automotive paint lines, for instance.